Sonic the Hedgehog 2 (16-bit)
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| Sonic Community Hacking Guide Sonic the Hedgehog 2 (16-bit) |
|---|
| Art |
| Objects |
| Levels |
| Text |
| Music |
| RAM |
| Miscellaneous |
This is the Sonic Community Hacking Guide for Sonic the Hedgehog 2. Originally based on Nemesis and saxman's guides, this document has grown to outclass those two documents in most ways, and is now preferred over the original guides (which were written three or four years ago with limited knowledge of the game's code). This is due to the updating of those documents to give them a living, breathing nature.
Miscellaneous
Pieces of the guide not big enough for their own page should be left here.
Game Configuration
| Offset | Description |
|---|---|
| $3CD2 | Enable level select |
| $3C79 | Starting lives for player 1 |
| $41CC | How to determine how many rings to start with |
| $41D0 | How to determine how much time starts on the timer |
| $142F8 | Order that the levels come in |
| $1600C | Object code pointers |
Each of the object code pointers are in 32-bits. They locate where the code for the object starts in the ROM. It starts with object 01 (Sonic) and goes in order from there. You will find a total of 220 pointers. These are useful if you want to create your own object code, or if you want to make one object into another. Check out the object list to see what each object is.
| Offset | Description |
|---|---|
| $16398 | Amount of gravity player has (16-bit) |
| $19FA2 | Max speed (16-bit) |
| $19FA8 | Acceleration (16-bit) |
| $19FAE | Slow down speed (16-bit) |
| $1A0E8 | Invincibility time (16-bit) |
| $1A122 | Max speed after super sneakers wear off (16-bit) |
| $1A122 | Acceleration after super sneakers wear off (16-bit) |
| $1A12E | Slow down speed after super sneakers wear off (16-bit) |
| $1A1B8 | Max speed under water (16-bit) |
| $1A1BE | Acceleration under water (16-bit) |
| $1A1C4 | Slow down speed under water (16-bit) |
| $1A5BD | Use this animation when looking down |
| $1A5D5 | How far to look down (player Y - input value) (16-bit) |
| $1AA5C | Jump height (16-bit) |
| $1AC47 | Do Spin Dash if this frame is shown |
| $1B1BE | Flash time after hit (16-bit) |
| $1B8A4 | Stop Tails from going to the left when end level sign is active (16-bit) |
| $1F1FC | Rings needed for special stage (16-bit) |
| $4082F | Specify the minute that causes "TIME" to flash red |
| $40DED | Max minutes of timer |
| $40DF9 | Max middle seconds of timer |
| $42594 | Art/mapping pointers for levels |
Each full level has 3 pointers. However, the pointers are 24-bits in size. The extra 8-bits in each pointer has a unique function. These are known as 'flags'. The pointers will define mapping sets, as well as art for a specific level. In total, 12 bytes are used per level. Here is what each flag/pointer does.
Flag 1 - Primary level PLC number
Pointer 1 - Level 8x8 art
Flag 2 - Secondary level PLC number
Pointer 2 - 16x16 mappings
Flag 3 - Palette number
Pointer 3 - 128x128 mappings.
Cheats editing
In this section, you can change any of the cheat codes to whatever you want them to be.
| Offset | Description |
|---|---|
| $3DEE | Tails / Miles switch |
| $97B2 | Level select / slow motion (example) |
| $97B7 | 14 continues (example) |
| $97BC | Debug mode (example) |
| $97C5 | Super Sonic (example) |
These codes (except for the first one listed) use the regular sound 00-7F format, not the 80-FF format that the regular sound pointers use. Also, you can make these codes as long as you want. Simply use '00' to tell the game that the code ends there. If you make the very first sound to play in the code sequence a '00', it will then require you to play that sound along with the rest of the code.
The first code (Tails / Miles switch) is based on the output of Sega's standard 3-button controller input routine:
| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | (this is a byte represented in bits) |
| S | A | C | B | R | L | D | U | (these are the bits translated to show what each key is) |
If you want to relocate some of these cheat codes to another area of the ROM, just change these address pointers.
| Offset | Description |
|---|---|
| $3DB6 | Tails / Miles switch cheat pointer |
| $9164 | Level select / slow motion cheat pointer |
| $916A | 14 continues cheat pointer |
| $9574 | Debug mode cheat pointer |
| $957A | Super Sonic cheat pointer |
Debug Mode
This will allow you to change the objects available in each of level when using debug mode. Each object uses 8 bytes to reference it in debug mode. Here are the notes you need to modify these references.
FORMAT:
#1 #2 #3 #4 #5 #6 #7 #8
1 - Object value
2 - ??? (usually 01)
3 + 4 - Size of selection
5 - Object type
7 +8 - Sprites for selection
You can use #3, #4, #7, and #8 for porting a selection sprite. Now, you need to know how the game understands how many sprites to read for a level. Each set of objects has a 2 byte header. Together, both bytes define how many objects should be available in debug mode. The first byte should probably stay 00 unless you want more than 255 objects! Now, you just need to know where the section is that tells what sprite set is used for what level.
041D0C - 16-bit address pointers for each level
Here are some of the objects that are listed and their locations
Default
041D30 - Ring
041D38 - Warp Monitor
Emerald Hill
041D42 - Ring
041D4A - Warp Monitor
041D52 - Starpost
Demo Recording
To show off a game, developers record demos. Many other people like to record their own demos too when it's possible. This is one of the fun things you can do in the Sonic 2 ROM.
| Offset | Description |
|---|---|
| $3D4E | Number of demos to play |
| $3DAC | Levels that are played during demo sequence |
| $42AA | Number of frames that a demo plays (16-bit) |
| $4948 | 32-bit address pointers for each level |
| $4CA8 | Demo for EHZ (Sonic) |
| $4D08 | Demo for EHZ (Tails) |
| $4D68 | Demo for CNZ |
| $4DD8 | Demo for CPZ |
| $4E38 | Demo for ARZ |
FORMAT:
#1 #2
1 - Keys pressed
2 - Frame count
For keys pressed, you simply need to know the Motorola key format:
| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | (this is a byte represented in bits) |
| S | A | C | B | R | L | D | U | (these are the bits translated to show what each key is) |
With a 1, that means the button is being used (on) and with a 0, the button isn't being used.
References